CN107667124B

CN107667124B - Process for producing fluoropolymer-based latex with mechanical stability

Info

Publication number: CN107667124B
Application number: CN201680031133.2A
Authority: CN
Inventors: V·劳里; Y-S·常
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2015-04-07
Filing date: 2016-04-04
Publication date: 2020-03-06
Anticipated expiration: 2036-04-04
Also published as: WO2016162291A1; KR102695682B1; EP3280749A1; US10414879B2; EP3280749B1; KR20170134594A; CN107667124A; US20180105650A1

Abstract

The present disclosure relates to a polymerization process wherein an emulsifier is introduced in the initial batch as well as during continuous feeding to provide improved mechanical stability of the resulting latex. Improved soap coverage can also be achieved during the polymerization process.

Description

Process for producing fluoropolymer-based latex with mechanical stability

RELATED APPLICATIONS

This application claims priority and benefit of U.S. application 62/144,091, "Process To product Fluorophenol-based latex with Improved Mechanical Stability" (filed on 7/4/2015), the entire contents of which are incorporated herein by reference for any and all purposes.

Technical Field

The present disclosure relates to methods, processes and techniques for preparing non-creamed styrene-acrylonitrile copolymer (SAN) encapsulated Polytetrafluoroethylene (PTFE) latex (TSAN latex) with improved latex mechanical stability. In addition, the present disclosure relates to compositions and articles comprising the compositions prepared by the methods described herein.

Background

PTFE-containing polymers are used as antidrip additives in the manufacture of flame-retardant thermoplastics. To improve the handling and compatibility of PTFE with other polymer matrices, an unsaturated SAN monomer is added to a fluoropolymer (e.g., PTFE) dispersion to produce a partially SAN encapsulated PTFE (tsan) polymer, resulting in an anti-drip additive, by an aqueous emulsion polymerization process. The encapsulation of PTFE as core particles using SAN as a shell to form the resulting TSAN composite polymer has at least two benefits: it minimizes premature fibrillation of the PTFE particles during the coagulation process used to recover the TSAN latex, and the resulting powdered TSAN latex has improved flowability.

Disclosure of Invention

With the existing PTFE encapsulation methods, it can prove difficult to produce stable TSAN latex. Formation of excess free SAN particles rather than TSAN particles with a core/shell TSAN composite structure can lead to unstable TSAN latexes. Further, if the latex dispersion is allowed to stand without stirring or agitation for a long period of time before coagulation, the dispersion can separate because the PTFE has a higher density than water (e.g., 2.4 grams per cubic centimeter (2.4g/cc) as compared to 1 g/cc). Such unstable latexes may be susceptible to premature coagulation or creaming through shear forces. To help obtain a homogeneous composition of TSAN powder after the coagulation process, an additional amount of emulsifying surfactant or soap is added to the dispersion to stabilize the TSAN latex after the dispersion polymerization. The additional soap may help prevent the dispersion from undergoing phase separation (creaming) and enhance the mechanical stability of the TSAN latex after polymerization.

Thus, unstable TSAN latex production can lead to problems such as latex separation (creaming) or TSAN powder with inconsistent PTFE content and eventual material loss or off-spec product, etc.

There is a need in the market for new SAN encapsulation processes that can produce paste-free TSAN latex without the addition of large amounts of soap. There is also a need in the marketplace for new processes that allow the production of TSAN latex over a longer period of time while maintaining a stable and homogeneous TSAN latex. The present disclosure addresses these and other shortcomings of the prior art.

Drawings

The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects and, together with the description, serve to explain the principles of the disclosure.

FIG. 1 shows various undiluted TSAN latexesLUMiSizer for phase separation rate of dispersions in percent transmission per second^TMA graph of the data.

FIG. 3 is a plot of viscosity and pH versus agitation time for a sample of commercially available TSAN latex.

Fig. 4 is a plot of viscosity and pH versus agitation time for TSAN latex samples in accordance with aspects of the present disclosure.

Additional advantages of the disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosure. The advantages of the disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.

Detailed description of illustrative embodiments

The present disclosure may be understood more readily by reference to the following detailed description of the disclosure and the examples included therein.

In various aspects, the present disclosure provides an aqueous emulsion polymerization process configured to provide a stable TSAN latex after polymerization is complete without the introduction of additional surfactants. The polymerization process may include a process sequence designed to graft one or more polymers onto a fluoropolymer-based seed, thereby encapsulating the PTFE.

The process disclosed herein can provide stable, uniform TSAN powders with consistent PTFE composition. In further aspects of the disclosure, the amount and charging sequence of soap and/or initiator may be varied to provide stable TSAN latex. More specifically, stable TSAN latexes as disclosed herein may have improved mechanical stability characterized by a slower rate of separation of the phases.

In one aspect, the process may include a polymerization process to provide a stable TSAN latex, followed by isolation of the TSAN resin by a coagulation process. The polymerization process may include an initial charge of reactants to the reaction vessel in combination with a subsequent feed of reactants to the reaction vessel. In one example, the initial charge of reactants may comprise a PTFE dispersion, water, monomer, and Tallow Fatty Acid (TFA) soap, which is heated to a suitable temperature and allowed to pretreat for a period of time in advance. As another example, as the temperature increases, a continuous feed of reactants may comprise the remaining monomers and initiator to provide a TSAN latex. Coagulation may include adding acid and water to the latex resulting from the polymerization reaction. The resulting wet resin may then be isolated and dried.

In one aspect, the method may consist essentially of: polymerization process to provide stable TSAN latex, followed by isolation of TSAN resin by coagulation process. The polymerization process may include an initial charge of reactants to the reaction vessel in combination with a subsequent feed of reactants to the reaction vessel. In one example, the initial charge of reactants may comprise a PTFE dispersion, water, monomer, and Tallow Fatty Acid (TFA) soap, which is heated to a suitable temperature and allowed to pretreat for a period of time in advance. As another example, as the temperature increases, a continuous feed of reactants may comprise the remaining monomers and initiator to provide a TSAN latex. Coagulation may include adding acid and water to the latex resulting from the polymerization reaction. The resulting wet resin may then be isolated and dried.

In various aspects, the present disclosure relates to latex polymerization systems for preparing latexes that exhibit mechanical stability. The latex polymerization system may include a reaction vessel that receives an initial charge comprising an aqueous dispersion of polytetrafluoroethylene, a portion of a predetermined amount of unsaturated monomer, a portion of a predetermined amount of soap. The contents of the vessel can be heated to between 54.4 ℃ (130 ° F) and 60 ℃ (140 ° F) and the resulting dispersion allowed to pre-treat in the vessel for 15 minutes. A continuous feed may then be introduced into the reaction vessel, the continuous feed comprising the remaining portion of the unsaturated monomer, the remaining portion of the soap, and the redox initiator system. During continuous feed, when about fifty weight percent of the unsaturated monomer is introduced to the reaction vessel, the contents of the vessel can be heated to between 54.4 ℃ (150 ° F) and 60 ℃ (140 ° F). The contents of the vessel can be cooled to provide a copolymer encapsulated polytetrafluoroethylene latex dispersion in which the latex exhibits mechanical stability such that the latex does not undergo phase separation after at least 100 hours of agitation at 200 revolutions per minute (rpm). The resulting latex dispersion can be coagulated to provide a copolymer resin.

Polymerization process

In one aspect, the polymerization process may involve combining PTFE, more specifically PTFE dispersions (e.g., aqueous dispersions), with SAN copolymers. The combination of PTFE and SAN may facilitate or enable the formation or preparation of an intermediate latex product (e.g., SAN encapsulated PTFE latex). The amount of soap and/or initiator and the order of charging can determine the stability of the TSAN latex produced and the homogeneity of the TSAN powder end product with consistent PTFE.

The polymerization process may include charging a reaction vessel (hereinafter referred to as a vessel) with an aqueous dispersion of PTFE, water, the selected monomer, and a surfactant, i.e., soap. The contents of the vessel may be pre-treated for at least 15 minutes prior to introducing the continuous feed of reactants. The continuous feed of reactants may include the remaining monomer and initiator system, during which the temperature of the contents of the vessel may be increased. In one example, a copolymer of acrylonitrile and styrene (i.e., a SAN copolymer) and a redox initiator system comprising an initiator and an activator (i.e., a combination of an oxidizing agent and a reducing agent) can be introduced into the vessel in a continuous feed.

In various aspects, the polymerization process can be carried out in a vessel, such as a closed reactor. The size of the container may range from, for example, 1 liter up to 4,921 liters (1,300 gallons). It should be understood that other vessels and/or reactors of different volumes may also be used in the polymerization process and may be readily and/or conveniently scaled up for industrial manufacture or production of SAN encapsulated PTFE-based latex (TSAN latex).

A number of monomers and reactants can be used in the polymerization process to produce TSAN polymers, including ethylenically unsaturated monomers, preferably styrene and acrylonitrile; surfactants such as fatty acid salts; and redox or non-redox initiators. The relative amounts and/or concentrations of one or more monomers or reactants used in the polymerization process can be selected and varied, for example, depending on the target or desired relative component compositions of the intermediates formed by the polymerization process and/or the target rates of reaction.

In certain aspects, the aqueous dispersion may be introduced into the vessel as an initial charge. An aqueous dispersion comprising 200 parts by weight (pbw) or about 200pbw may comprise water, preferably demineralised water, in an amount of 150pbw or about 150 pbw; from about 45 to about 55pbw PTFE per 100pbw of dispersion, or from about 45 to about 55pbw PTFE; and from about 1 to about 5, or from about 1 to about 5pbw of fatty acid soap per 100pbw of dispersion. In one example, the aqueous dispersion may comprise 50pbw, or about 50pbw, demineralized water per 100pbw of dispersion, and 4pbw, or about 4pbw, Tallow Fatty Acid (TFA) soap salt per 100pbw of dispersion.

In various aspects of the present disclosure, the contents of the containers may be combined to form a uniform PTFE dispersion. A stirrer may be used to stir the contents of the vessel. In other examples, an agitator may be used to combine the contents. The mild agitation speed may be 120rpm or about 120rpm, depending on the size of the reactor vessel used.

In one aspect, the temperature of the contents of the vessel may be adjusted to a target temperature to facilitate the polymerization reaction. In one example, after the initial charge of PTFE dispersion, water, and soap of reactants is introduced into the vessel, the temperature of the vessel can be increased to about 57.8 ℃ (136 ° F). In some examples, the temperature may be raised to the desired temperature prior to addition of the monomer or optional activator.

In some aspects, the temperature of the contents of the vessel may be determined depending on the type of initiator system selected for the polymerization process. As another example, for a redox initiator system, the target temperature can be between about 54.4 ℃ (130 ° F) to about 71.1 ℃ (160 ° F). In another example, for a redox initiator system, the target temperature can be between 54.4 ℃ (130 ° F) and 71.1 ℃ (160 ° F). In another example, the target temperature may be 57.7 ℃, or about 57.7 ℃ (136 ° F).

In one aspect, the target temperature may be adjusted by using a heating system, such as a hot steam jacket system. Other heating systems, such as those known in the relevant art or heaters, may also be used to change and/or maintain the temperature of the container. Since the polymerization process can generate considerable heat, a cooling system can also be used. The cooling system may also include a jacket system. A device may be used to control the heating and cooling of the container and its contents. An exemplary device may be a thermocouple. The thermocouple may control heating and cooling by a software system or an integrated distributed control system. Thermocouples can be configured to measure the temperature of the jacket system water inlet and outlet.

In various aspects, the polymer or copolymer used to encapsulate the PTFE particles can be any polymer or copolymer obtained by free radical initiated emulsion polymerization of a monomer or mixture of monomers. As an example, a copolymer of acrylonitrile and styrene (SAN copolymer) and a redox initiator system can be used as the encapsulating polymer.

In one aspect, the reactants and activator can be introduced into the vessel immediately or substantially immediately upon reaching the desired or target temperature. During addition to the vessel, the temperature of the vessel can be maintained between 54.4 ℃ and 71.1 ℃, or between about 54.4 ℃ (130 ° F) and about 71.1 ℃ (160 ° F), such as at 60 ℃ (140 ° F) or about (60 ℃ (140 ° F). In several embodiments, upon reaching the desired or target vessel temperature (e.g., 60 ℃ (140 ° F) or about 60 ℃ (140 ° F)), styrene monomer and acrylonitrile monomer are each added to the vessel immediately or substantially immediately. More specifically, upon reaching a desired or target vessel temperature, predetermined amounts of styrene monomer and acrylonitrile monomer (or a specified percentage of the total or final amount of styrene monomer and acrylonitrile monomer) may first be added to the vessel. For example, upon reaching a desired or target vessel temperature (e.g., 60 ℃ or about 60 ℃ (140 ° F)), 5% to 20%, or about 5% to about 20% (e.g., 10% or about 10%) of the total or final amount of styrene monomer and acrylonitrile monomer can be immediately or substantially immediately added to the reactor to initiate the reaction at an initial stage.

When the temperature is raised and maintained at the target temperature (e.g., 54.4 ℃ (130 ° F) to 71.1 ℃ (160 ° F), or about 5 ℃Between 4.4 ℃ (130 ° F) and about 71.1 ℃ (160 ° F)), styrene monomer and acrylonitrile monomer can then each be added to the container as a solution. Alternatively, the catalyst may be added to the vessel as an aqueous solution after the reactor temperature is increased. Optionally, the catalyst may be a redox initiator system, such as a combination of: ferrous ion/Cumene Hydroperoxide (CHP), cumene hydroperoxide, ferrous sulfate (FeSO)₄) Tetrasodium pyrophosphate (TSPP) and a reducing sugar such as cerelose or fructose may be added to the vessel just prior to starting the continuous feed of monoethylenically unsaturated monomers. Preferably, the catalyst used in the polymerization process may be FeSO₄a/CHP redox initiator system.

In some aspects, the catalyst may comprise a catalyst system comprising an activator, a reducing agent, and an oxidizing agent. Activators may include ferrous compounds such as ferrous sulfate and tetrasodium pyrophosphate. The reducing agent may comprise a reducing sugar such as sirocco or fructose. The oxidizing agent may include cumene hydroperoxide.

The reactants of the present disclosure may include tallow fatty acid soap or soap emulsifiers. Fatty acid soaps may be used as emulsifiers for the latex polymerization process. The fatty acid soap may be water soluble. Exemplary tallow fatty acid soaps may include mixtures of fatty acids. Exemplary fatty acid soaps may include sodium palmitate, potassium laurate, sodium oleate, ammonium oleate, sodium myristate. In certain examples, the fatty acid soap may comprise a mixture of fatty acids derived from a porcine derived oil.

In various embodiments of the present disclosure, a monomer solution of styrene and acrylonitrile may be added to the vessel during each of the introduction of the catalyst and the introduction of the emulsifier into the vessel. More specifically, between 5% and 20%, or between about 5% and about 20%, for example 10% or about 10%, of a monomer solution of styrene and a monomer solution of acrylonitrile may be added simultaneously to a vessel with catalyst; and between 80% and 95%, or between about 80% and about 95%, for example 90% or about 90% (i.e. the remainder) of the two monomer solutions may be subsequently added simultaneously to the reactor.

In some aspects, appropriate molecular weight regulators (or chain transfer/activating agents) may be added to improve the properties of the final resin product. For example, in one example, the molecular weight regulator may be added at the initial batch charge of the reaction. Suitable activators include (C)₉-C₁₃) Alkyl mercaptan compounds such as tert-dodecyl mercaptan (TDDM) or nonyl mercaptan. The amount of molecular weight regulator may vary depending on the particular molecular weight regulator, the monomer or monomer mixture used, the initiator used, the polymerization conditions, and the like. Optionally, a chain transfer activator may be introduced into the reactor to reduce the molecular weight of the second polymer (e.g., SAN) formed during the polymerization process. In one example, the molecular weight regulator may be added at 0.1 to 3 parts by weight of the molecular weight regulator or about 0.1 to about 3 parts by weight of the molecular weight regulator per 100 parts by weight of the monomer. In a preferred embodiment, no activator is used.

After the initiator is added, after 30 minutes or about 30 minutes of initiation, the temperature of the vessel is increased, for example to 65.5 ℃ (150 ° F), or about 65.5 ℃ and held at that temperature until the addition of styrene and acrylonitrile monomers is complete. In one example, 31 to 34pbw, or about 31 to about 34pbw, of unsaturated styrene monomer and 11 to 14pbw, or about 11 to about 14pbw, of unsaturated acrylonitrile monomer per total weight of polymer may be continuously fed to the reactor. The monomers may be added to the reactor over a period of between 1.0 hour and 2.5 hours or between about 1.0 hour and about 2.5 hours, such as 1.5 hours or about 1.5 hours.

Once the feed is complete, the reactor is continuously stirred and mixed using a stirrer or agitator, stirring at 120rpm or about 120rpm and at 65.5 ℃ (150 ° F) or about 65.5 ℃ for 30 minutes or about 30 minutes, to achieve high conversion, e.g., greater than 97% or greater than about 97%.

Once the feed is complete, the contents of the vessel are stirred and/or agitated using a stirrer or agitator to mix the contents. Agitation may be continuous or periodic so that the contents of the vessel do not separate. In one aspect, the contents of the vessel can be stirred or agitated within 30 minutes or about 30 minutes and at a temperature of 65.5 ℃ to 71.1 ℃ or about 65.5 ℃ (150 ° F) to about 71.1 ℃ (160 ° F) to complete the conversion of the monomers to at least greater than about 97%. The polymerization process can result in the export of at least TSAN latex.

Additional predetermined amounts of styrene monomer and acrylonitrile monomer or the total or final amounts of styrene monomer and acrylonitrile monomer can then be added to the vessel over a period of between 1.0 hour and 2.5 hours, or from about 1.0 hour to about 2.5 hours, for example about 1.5 hours.

In several aspects, the surfactant and catalyst can be initially or continuously introduced into the vessel during the monomer charge for a period of between 1.0 hour and 2.5 hours, or between about 1 hour and about 2.5 hours, such as 1.5 hours, or about 1.5 hours. Examples of possible surfactants include fatty acid salts made from fatty acids and caustic solutions (e.g., KOH).

The reaction mixture may optionally include minor amounts, e.g., up to 5 weight percent (wt%), or up to about 5 wt%, of multi-ethylenically unsaturated "crosslinking" monomers, e.g., butylene glycol diacrylate, divinyl benzene, butylene glycol dimethacrylate, trimethylolpropane tri (meth) acrylate. As used herein, the term "polyethylenically unsaturated" refers to having two or more sites of ethylenic unsaturation per molecule.

In addition, a color stabilizer may be added. In several embodiments, the color stabilizer includes tetrasodium pyrophosphate (TSPP), Sodium Formaldehyde Sulfoxylate (SFS), and/or potassium hydroxide (KOH).

The contents of the container may then be cooled. In many aspects of the present disclosure, the polymerization process produces an intermediate product, more specifically a TSAN latex. The TSAN latex comprises SAN copolymer particles and TSAN particles having a PTFE-based core and a SAN-based shell surrounding, or at least substantially surrounding, the PTFE-based core.

The resulting TSAN polymer composition may comprise 45 to 55 wt%, or about 45 to about 55 wt% PTFE and 45 to 55 wt%, or about 45 to about 55 wt% SAN, wherein the weight ratio of acrylonitrile monomer to styrene monomer ranges from 20/80 to 30/70, about 20/80 to about 30/70.

After polymerization, a coagulation and drying process can be performed to provide a free-flowing TSAN powder. Coagulation of TSAN latex can be accomplished by introducing heated acid or salt solutions into the latex. The solution can be heated to a temperature of 95 ℃ (35 ° F) or about 95 ℃. The resulting mixture can be gently agitated and filtered, centrifuged and dried to produce the final dry TSAN powder.

Agglomeration method

The present disclosure further includes using or performing the agglomeration process after the polymerization process used to manufacture or produce the TSAN powder (i.e., the final or resulting product). The TSAN powder may be present in the solid state or at least substantially solid state. In several embodiments, the TSAN powder has increased compatibility with other plastic powders, thereby improving or increasing the ease and/or efficiency associated with mixing TSAN powder with other plastic powders, such as during a compounding process for making plastics or plastic-based products.

The TSAN latex produced by polymerization, e.g., as described herein, may then be subjected to a coagulation process, wherein the TSAN latex is exposed to a mixture of water and coagulant. During the agglomeration process, the fine particles agglomerate or clump together and accumulate at the top of the dispersion or settle at the bottom and can be separated or harvested by filtration methods.

The coagulant may include acids such as, but not limited to, acetic acid, sulfuric acid, and phosphoric acid, or salts such as calcium chloride, magnesium sulfate, and aluminum sulfate. SAN and TSAN particles co-agglomerate and precipitate to form large polymer agglomerates in an acid or salt solution and further harden at high temperatures.

In addition, a reactant such as sulfuric acid (H) may be added₂SO₄) As a coagulant. Optionally, a salt such as sodium chloride, sodium sulfate, ammonium acetate or other salt comprising a monovalent cation and a monovalent anion can be added to the reaction mixture followed by addition of a dilute acid such as sulfuric acid.

The TSAN latex can be introduced in a vessel containing an acid solution (about 1 to 2 parts aqueous sulfuric acid), and the contents of the vessel can be heated to 93.3 ℃ (200 ° F) or about 93.3 ℃ (200 ° F) with vigorous stirring. The solids content of the mixture is no greater than 20 wt.%, or no greater than about 20 wt.%. Complete introduction of TSAN latex takes 10 minutes, or about 10 minutes. The contents of the vessel form a slurry, and prior to centrifugation, the slurry can be continuously stirred at 93.3 ℃ (200 ° F) or about 93.3 ℃ for 20 minutes or about 20 minutes to form a wet powder. The wet powder can then be redispersed in whole water at a temperature of 54.4 ℃ (130 ° F) or about 54.4 ℃ (130 ° F) for 10 minutes or about 10 minutes to remove residual acid or salts. After centrifugation, the powder can be dried in a fluid bed dryer at a temperature of 60 ℃ (140 ° F) or about 60 ℃ (140 ° F) for 2 hours or about 2 hours. A free flowing powder having a final moisture content of less than 0.5% or less than about 0.5% can be obtained.

The agglomeration process produces the resulting product as TSAN powder. The powder is produced in the form of a suspension in water, a product or a powder. More specifically, TSAN powder may comprise solid particles having SAN particles and a PTFE-based core having a SAN-based shell surrounding, or at least substantially surrounding, the PTFE-based core.

In many embodiments, the agglomeration process occurs or can be carried out in a vessel, such as a 15 liter vessel. The volume or capacity of the vessel used in the coagulation process can be increased, for example, for the preparation or manufacture of TSAN latex on an industrial scale.

The coagulation process produces TSAN latex powder. The powder is produced in the form of a suspension in water, a product or a powder. More specifically, the TSAN latex powder comprises solid particles having a PTFE-based core and a SAN-based shell surrounding, or at least substantially surrounding, the PTFE-based core.

Latex stability

In addition, the present disclosure details novel configurations of temperatures, reactant combinations, relative reactant concentrations and/or amounts and/or durations during one or more portions of a polymerization process for making or producing TSAN latex (or intermediate products). This novel configuration of using temperature, combination of reactants, relative reactant concentrations and/or amounts and/or durations during one or more portions of the polymerization process can facilitate or enable the production of TSAN latex powders (or end products) having significantly, surprisingly and/or unexpectedly enhanced properties or characteristics.

In various aspects, the addition of soap in the initial charge and the feed charge to the polymerization vessel can improve the mechanical stability (MMS) of the TSAN latex produced. Mechanical stability may refer to the resistance of the latex to creaming or the phase separation of the latex. MMS can be expressed in terms of time, i.e., how long the latex can remain stable and resist creaming. This creaming can occur with the latex at rest or left for a period of time without agitation. The creaming effect can be attributed to the difference in density of the rubber particles present in the rubber latex and the solution in which the particles are dispersed. In one example, a TSAN latex polymerization process (in which soap is included in the initial charge and introduced into the continuous feed) may resist separation or creaming after agitation at 200rpm or about 200rpm for greater than 100 hours or greater than about 100 hours. Comparable TSAN latexes, in which soap is introduced only in the initial batch, can begin to creame in 10 hours or about 10 hours. As an example, a TSAN latex polymerization process in which the initial soap charge is 1.25pbw or about 1.25pbw and the soap feed is 2.75pbw, or about 2.75pbw, may resist creaming after more than 100 hours or more than about 100 hours of agitation, while the soap addition contains only 4pbw, or about 4pbw, of the polymerization of the initial batch charge may begin to creaming within 10 hours or within about 10 hours.

In another aspect, TSAN prepared according to the methods disclosed herein, wherein soap is introduced to the vessel in the initial charge and during continuous feed, the shelf life of the TSAN latex can be extended. The improvement in the stability of TSAN latex can be illustrated by an increased shelf life. The stability of a latex may refer to its ability to remain stable or its ability to resist droplet aggregation. Stability can therefore be observed by measuring the rate of phase separation of the dispersion. For example, the rate of phase separation can be observed by the change in particle size of the emulsion (e.g., latex) after being held under controlled conditions for a specified period of time or after being exposed to a particular environmental stress.

Dimensionless instability index can be used as latex stabilityIs measured. As an example, the instability index may be determined using a dispersion analyzer, such as a LUMisizer^TMTo determine, which combines a Near Infrared (NIR) probe with an analytical centrifuge to determine the separation and sedimentation phenomena in the latex. The instability index indicates the degree of instability of the latex emulsion, and can be measured by calculating the difference in percent transmittance of light through the sample over a given period of time. These results can then be normalized to the theoretical maximum percent transmission. The set of transmission curves observed at different positions along the cuvette can be reduced to a single curve by appropriate integration of each of the transmission percentage distributions. Thus, the instability index can be calculated from the slope of the transmission curve according to the following equation:

delta transmission% (or backscatter) ═ f (time)

Thus, the lower the instability index, the more stable the dispersion and the longer the shelf life. The value of the instability index may be in the range of 0 to 1.0, with a value of zero indicating no instability. The horizontal segment of the curve may indicate that the transmission profile of the latex sample under consideration with respect to the test container is constant over the time interval under consideration. The ramp back traces back to sedimentation/creaming, i.e. latex instability.

The instability index can therefore reflect the viscosity change of TSAN latex under prolonged agitation. When a given latex maintains its viscosity under prolonged agitation, little or no creaming occurs and the latex is more stable. TSAN latex prepared according to the processes disclosed herein may have an instability index of 0.0003 or about 0.0003, while TSAN latex obtained from processes in which soap is added only in the initial charge may have an instability index of 0.0007 or about 0.0007.

In further aspects of the disclosure, introducing the activator solution during continuous feeding of the vessel may improve mechanical stability as compared to introducing during continuous feeding. For example, addition of the activator solution via a continuous feed may provide an MMS of 75 minutes or about 75 minutes, as compared to 7 minutes or about 7 minutes when the activator solution is introduced only in the initial batch feed.

Soap coverage of the polymerization process can also be improved by using separate feeds of soap and adding the activator solution via a continuous feed. Soap coverage may relate to the amount of emulsifier (soap) sufficient to prevent aggregation of the polymer particles in the polymerization process. In one embodiment, soap coverage may be 69%, or about 69%, in the case of a separate addition of soap (1.25pbw in the initial charge, 2.75pbw in the continuous feed), compared to 55%, or about 55%, in the case of soap addition at 4 parts by weight in the initial batch only. As a further example, where the soap feed is split between an initial (1.25pbw) and continuous feed (2.75pbw), the continuous feed activator addition may increase the soap coverage to 69.3% or about 69.3%; whereas a polymerization process that only incorporates the activator in the initial batch may have a soap coverage of 60.3% or about 60.3%.

Thus, the separate initial and feed charge soaps combined with the introduction of activator solution by continuous feed can improve the stability of TSAN latex. More specifically, 1.25pbw of the initial soap charge and 2.75pbw of the continuous feed in combination with introducing the activator solution as a continuous feed may provide an MMS of greater than 30 minutes or greater than about 30 minutes. Indeed, an initial soap charge of 1.25pbw and a continuous feed of 2.75pbw may provide an MMS of greater than 30 minutes or greater than about 30 minutes, even when the activator solution is introduced in the initial batch.

The TSAN powder provided by the various embodiments of the present disclosure may be used to make plastics or plastic products, including those having smooth or substantially smooth surfaces. When used as an additive, the TSAN powders of particular embodiments of the present disclosure provide improved or enhanced processability and/or improved mechanical properties (e.g., increased abrasion resistance or lower surface roughness), are easy to handle and work with (i.e., have enhanced handleability and/or handleability), and may exhibit enhanced flow characteristics and reduced agglomeration, as compared to existing PTFE powders. Additionally, TSAN powder can be used or combined with other plastic-based resins to produce flame retardant compositions with flame retardant properties.

Definition of

As used herein, the terms "about" and "at or about" mean that the amount or value in question may be approximately or about the same value specified as some other value. It is generally understood that, as used herein, it is a nominal value representing a ± 10% variation, unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that the amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. Generally, an amount, size, formulation, parameter or other quantity or characteristic is "about" or "approximately" whether or not explicitly stated. It is understood that where "about" is used before a quantitative value, a parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

Ranges may be expressed herein as from one particular value and/or to another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both to the other endpoint, and independently of the other endpoint. It is also understood that a plurality of values are disclosed herein, and that each value is also disclosed herein as "about" that particular value, in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed. It will also be understood that each unit between two particular units is also disclosed. For example, if 10 and 15 are disclosed, 11, 12, 13 and 14 are also disclosed.

As used herein, the terms "weight percent," "wt%" and "wt%" may be used interchangeably and refer to the weight percent of a given component based on the total weight of the composition, unless otherwise specified. That is, all wt% values are based on the total weight of the composition, unless otherwise specified. It is understood that the sum of the wt% values of all components in the disclosed compositions or formulations is equal to 100.

Unless otherwise stated, all test standards are the most current standards in force at the time of filing this application.

Each of the materials disclosed herein are commercially available and/or methods for their preparation are known to those skilled in the art.

As used in the specification and claims, the term "comprising" may include embodiments "consisting of and" consisting essentially of. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In this specification and the claims that follow, reference will be made to a number of terms that are defined herein.

It is to be understood that the disclosed and described compounds, compositions, articles, systems, devices, and/or methods of the present invention are not limited to particular synthetic methods, or to particular reactants, as such may, of course, vary, unless otherwise specified. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, the exemplary methods and materials are now described.

Further, it will be understood that, unless explicitly stated otherwise, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a particular order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is not possible to infer an order from any aspect. This applies to any possible ambiguous interpretation grounds, including: logical considerations regarding the arrangement of steps or operational flow; simple meaning from grammatical organization or punctuation; and the number or type of embodiments described in the specification.

Aspect(s)

In various aspects, the present disclosure pertains to and includes at least the following aspects.

Aspect 1. A method, comprising: an initial charge comprising: introducing an aqueous dispersion of polytetrafluoroethylene into a vessel; introducing styrene or acrylonitrile monomer into the vessel; introducing soap into the container; heating the contents of the container to between about 54.4 ℃ (130 ° F) to about 60 ℃ (140 ° F); and allowing the dispersion to pre-treat in the vessel for about 15 minutes; wherein the initial charge comprises introducing into the container about 45 to about 55 parts by weight of polytetrafluoroethylene, about 5 to about 20 parts by weight of styrene or acrylonitrile monomer, and about 1 to about 5 parts by weight of soap, and wherein the combined parts by weight value of all components does not exceed 100 parts by weight; a continuous feed comprising introducing styrene and acrylonitrile monomers; introducing a redox initiator system; introducing a soap; and heating the contents of the container to between about 65.6 ℃ (150 ° F) and about 71.1 ℃ (160 ° F) when about fifty weight percent of styrene monomer, acrylonitrile monomer, and copolymer of styrene and acrylonitrile are introduced to the container, wherein the continuous feed comprises about 31 to about 34 parts by weight of styrene monomer, about 11 to about 14 parts by weight of acrylonitrile monomer, and including about 0.1 to about 2 parts by weight of redox initiator system, and about 1 to about 5 parts by weight of soap introduced over a period of about 1 to about 2.5 hours; wherein the polymerization process produces a styrene-acrylonitrile copolymer encapsulated polytetrafluoroethylene latex dispersion; and coagulating the styrene-acrylonitrile copolymer encapsulated polytetrafluoroethylene latex dispersion, wherein the latex is exposed to a heated mixture of water and a coagulant to produce an output slurry.

Aspect 2. A method consisting essentially of: the initial charge comprises: introducing an aqueous dispersion of polytetrafluoroethylene into a vessel; introducing styrene or acrylonitrile monomer into the vessel; introducing soap into the container; heating the contents of the container to between about 54.4 ℃ (130 ° F) to about 60 ℃ (140 ° F); and allowing the dispersion to pre-treat in the vessel for about 15 minutes; wherein the initial charge comprises introducing into the container about 45 parts by weight to about 55 parts by weight polytetrafluoroethylene, about 5 parts by weight to about 20 parts by weight styrene or acrylonitrile monomer, and about 1 part by weight to about 5 parts by weight soap, and wherein the combined parts by weight value of all components does not exceed 100 parts by weight; the continuous feed comprises: introducing styrene and acrylonitrile monomers; introducing a redox initiator system; introducing a soap; and heating the contents of the vessel to between about 65.6 ℃ (150 ° F) and about 71.1 ℃ (160 ° F) when about fifty weight percent of the styrene monomer, the acrylonitrile monomer, and the copolymer of styrene and acrylonitrile are introduced to the vessel, wherein the continuous feed comprises about 31 to about 34 parts by weight of the styrene monomer, about 11 to about 14 parts by weight of the acrylonitrile monomer, and including about 0.1 to about 2 parts by weight of the redox initiator system, and about 1 to about 5 parts by weight of the soap introduced over a period of about 1 hour to about 2.5 hours; wherein the polymerization process produces a styrene-acrylonitrile copolymer encapsulated polytetrafluoroethylene latex dispersion; and coagulating the styrene-acrylonitrile copolymer encapsulated polytetrafluoroethylene latex dispersion, wherein the latex is exposed to a heated mixture of water and a coagulant to produce an output slurry.

Aspect 3. The method of any of aspects 1-2, wherein the styrene or acrylonitrile monomer added in the initial charge is a fraction of a predetermined total amount of styrene or acrylonitrile monomer.

Aspect 4. The method of aspect 3, wherein introducing the continuous feed of styrene and acrylonitrile monomer comprises introducing a remaining portion of the styrene or acrylonitrile monomer.

Aspect 5. The process of any of aspects 1-4, wherein styrene or acrylonitrile is added to the initial feed after heating the contents of the vessel to about 135 ° F.

Aspect 6. The method of any of aspects 1-5, further comprising combining a chain transfer or crosslinking agent with the incorporation of the aqueous dispersion, the styrene monomer, and the soap.

Aspect 7. The method of any of aspects 1-6, wherein the soap comprises tallow fatty acid soap.

Aspect 8. The method of any of aspects 1-7, wherein the redox initiator system comprises a redox reactant and an activator.

Aspect 9. The method of aspect 8, wherein the redox initiator system comprises a mixture of cumene hydroperoxide in combination with sugar, ferrous sulfate, and tetrasodium pyrophosphate.

Aspect 10. The process of any of aspects 1-9, wherein the initial batch charge or continuous feed comprises a molecular weight regulator.

Aspect 11. The process of any of aspects 1-10, wherein the continuous feed of styrene and acrylonitrile monomers is introduced in a predetermined amount based on the amount introduced in the initial charge.

Aspect 12. The method of any of aspects 1-11, wherein the condensing agent is sulfuric acid.

Aspect 13. The method of any of aspects 1-12, wherein the output slurry is dried to produce a resin powder.

Aspect 14. A method, comprising: introducing an initial charge into a reaction vessel, said initial charge comprising an aqueous dispersion of polytetrafluoroethylene, a portion of a predetermined amount of unsaturated monomer, a portion of a predetermined amount of soap; heating the contents of the vessel to between about 54.4 ℃ (130 ° F) to about 60 ℃ (140 ° F) and allowing the resulting dispersion to pre-treat in the vessel for about 15 minutes; introducing a continuous feed to the reaction vessel, the continuous feed comprising a remaining portion of the unsaturated monomer, a remaining portion of the soap, and a redox initiator system; heating the contents of the vessel to between about 65.6 ℃ (150 ° F) and about 71.1 ℃ (160 ° F) when about fifty weight percent of the unsaturated monomer is introduced to the reaction vessel; cooling the contents of the vessel to provide a copolymer encapsulated polytetrafluoroethylene latex dispersion, wherein the latex exhibits enhanced mechanical stability such that the latex does not undergo phase separation after at least 100 hours of agitation at 200 rpm; coagulating the latex dispersion to provide a copolymer resin.

Aspect 15. A method consisting essentially of: introducing an initial charge into a reaction vessel, said initial charge comprising an aqueous dispersion of polytetrafluoroethylene, a portion of a predetermined amount of unsaturated monomer, a portion of a predetermined amount of soap; heating the contents of the vessel to between about 54.4 ℃ (130 ° F) to about 60 ℃ (140 ° F) and allowing the resulting dispersion to pre-treat in the vessel for about 15 minutes; introducing a continuous feed to the reaction vessel, the continuous feed comprising a remaining portion of the unsaturated monomer, a remaining portion of the soap, and a redox initiator system; heating the contents of the vessel to between about 65.6 ℃ (150 ° F) and about 71.1 ℃ (160 ° F) when about fifty weight percent of the unsaturated monomer is introduced to the reaction vessel; cooling the contents of the vessel to provide a copolymer encapsulated polytetrafluoroethylene latex dispersion, wherein the latex exhibits enhanced mechanical stability such that the latex does not undergo phase separation after at least 100 hours of agitation at 200 rpm; coagulating the latex dispersion to provide a copolymer resin.

Aspect 16. An aspect of method 14, wherein the initial charge comprises about 45 parts by weight to about 55 parts by weight polytetrafluoroethylene, about 1 part by weight to about 20 parts by weight styrene, and about 1 part by weight to about 5 parts by weight soap.

Aspect 17. The method of any of aspects 14-16, wherein the initial charge of soap is about 1.25 parts by weight and the continuous charge of soap is about 2.75 parts by weight.

Aspect 18. The method of any of aspects 14-17, wherein the unsaturated monomer is styrene or acrylonitrile.

Aspect 19. The method of any of aspects 14-18, wherein the unsaturated monomer is added to the initial charge after the vessel is heated to about 135 ° F.

Aspect 20. The method of any of aspects 14-19, further comprising combining a chain transfer or crosslinking agent with the incorporation of the aqueous dispersion, the styrene monomer, and the soap.

Aspect 21. The method of any of aspects 14-20, wherein the soap comprises tallow fatty acid soap.

Aspect 22. The method of any of aspects 14-21, wherein the redox initiator system comprises a mixture of cumene hydroperoxide in combination with sugar, ferrous sulfate, and tetrasodium pyrophosphate.

Aspect 23. The process of any of aspects 14-22, wherein the initial charge or continuous feed comprises a molecular weight regulator.

Aspect 24. The method of any of aspects 14-23, wherein the condensing agent is sulfuric acid.

Aspect 25. The method of any of aspects 1-24, wherein the latex comprises from about 25 wt.% to about 65 wt.% solids.

Aspect 25. A method, comprising: the initial charge comprises: introducing an aqueous dispersion of polytetrafluoroethylene into a vessel; introducing styrene or acrylonitrile monomer into the vessel; introducing soap into the container; heating the contents of the container to between 54.4 ℃ (130 ° F) and 60 ℃ (140 ° F); and allowing the dispersion to pre-treat in the vessel for about 15 minutes; wherein the initial charge comprises introducing into the vessel 45 to 55 parts by weight of polytetrafluoroethylene, 5 to 20 parts by weight of styrene or acrylonitrile monomer, and 1 to 5 parts by weight of soap, and wherein the combined parts by weight value of all components does not exceed 100 parts by weight; the continuous feed comprises: introducing styrene and acrylonitrile monomers; introducing a redox initiator system; introducing a soap; and heating the contents of the vessel to between 65.6 ℃ (150 ° F) and 71.1 ℃ (160 ° F) when about fifty weight percent of the styrene monomer, the acrylonitrile monomer, and the copolymer of styrene and acrylonitrile are introduced to the vessel, wherein the continuous feed comprises 31 to 34 parts by weight of the styrene monomer, 11 to 14 parts by weight of the acrylonitrile monomer, 0.1 to 2 parts by weight of the redox initiator system, and 1 to 5 parts by weight of the soap introduced over a period of 1 to 2.5 hours; wherein the polymerization process produces a styrene-acrylonitrile copolymer encapsulated polytetrafluoroethylene latex dispersion; and coagulating the styrene-acrylonitrile copolymer encapsulated polytetrafluoroethylene latex dispersion, wherein the latex is exposed to a heated mixture of water and a coagulant to produce an output slurry.

Aspect 26. The method of aspect 25, wherein the styrene or acrylonitrile monomer added in the initial charge is part of a predetermined total amount of styrene or acrylonitrile monomer.

Aspect 27. The method of aspect 26, wherein introducing the continuous feed of styrene and acrylonitrile monomer comprises introducing a remaining portion of the styrene or acrylonitrile monomer.

Aspect 28. The process of aspect 27, wherein styrene or acrylonitrile is added to the initial feed after heating the contents of the vessel to 57.2 ℃ (135 ° F).

Aspect 29. The method of any of aspects 25-28, further comprising combining a chain transfer or crosslinking agent with the incorporation of the aqueous dispersion, the styrene monomer, and the soap.

Aspect 30. The method of any of aspects 25-29, wherein the soap comprises tallow fatty acid soap.

Aspect 31. The method of any of aspects 25-30, wherein the redox initiator system comprises a redox reactant and an activator.

Aspect 32. The method of aspects 25-31, wherein the redox initiator system comprises a mixture of cumene hydroperoxide in combination with sugar, ferrous sulfate, and tetrasodium pyrophosphate.

Aspect 33. The process of any of aspects 25-32, wherein the initial batch charge or continuous feed comprises a molecular weight regulator.

Aspect 34. The process of any of aspects 25-33, wherein the continuous feed of styrene and acrylonitrile monomers is introduced in a predetermined amount based on the amount introduced in the initial charge.

Aspect 35. The method of any of aspects 25-34, wherein the condensing agent is sulfuric acid.

Aspect 36. The method of any of aspects 25-35, wherein the output slurry is dried to produce a resin powder.

Aspect 37. A method, comprising: introducing an initial charge into a reaction vessel, said initial charge comprising an aqueous dispersion of polytetrafluoroethylene, a portion of a predetermined amount of unsaturated monomer, a portion of a predetermined amount of soap; heating the contents of the vessel to between 54.4 ℃ (130 ° F) and 60 ℃ (140 ° F) and allowing the resulting dispersion to pretreat in the vessel for 15 minutes; introducing a continuous feed to the reaction vessel, the continuous feed comprising a remaining portion of the unsaturated monomer, a remaining portion of the soap, and a redox initiator system; heating the contents of the vessel to between 54.4 ℃ (150 ° F) and 60 ℃ (140 ° F) when about fifty weight percent of the unsaturated monomer is introduced to the reaction vessel; cooling the contents of the vessel to provide a copolymer encapsulated polytetrafluoroethylene latex dispersion, wherein the latex exhibits enhanced mechanical stability such that the latex does not undergo phase separation after stirring at 200rpm for at least 100 hours; coagulating the latex dispersion to provide a copolymer resin.

Aspect 38. The method of aspect 37, wherein the initial charge comprises 45 to 55 parts by weight polytetrafluoroethylene, 1 to 20 parts by weight styrene, and 1 to 5 parts by weight soap.

Aspect 39. The method of any of aspects 37-38, wherein the initial charge of soap is 1.25 parts by weight and the continuous charge of soap is 2.75 parts by weight.

Aspect 40. The method of any of aspects 37-39, wherein the unsaturated monomer is styrene or acrylonitrile.

Aspect 41. The method of any of aspects 37-40, wherein the unsaturated monomer is added to the initial charge after heating the vessel to 57.2 ℃ (135 ° F).

Aspect 42. The method of any of aspects 37-41, further comprising combining a chain transfer or crosslinking agent with the incorporation of the aqueous dispersion, the styrene monomer, and the soap.

Aspect 43. The process of any of aspects 37-42, wherein the initial charge or continuous feed comprises a molecular weight regulator.

Aspect 44. The method of any of aspects 37-43, wherein the latex comprises 25 wt.% to 65 wt.% solids.

Aspect 45. A latex polymerization system comprising: a reaction vessel receiving an initial charge comprising an aqueous dispersion of polytetrafluoroethylene, a portion of a predetermined amount of unsaturated monomer, a portion of a predetermined amount of soap; the contents of the vessel, which were heated to between 54.4 ℃ (130 ° F) and 60 ℃ (140 ° F) and the resulting dispersion was allowed to pre-treat in the vessel for 15 minutes; a continuous feed introduced to the reaction vessel, the continuous feed comprising a remaining portion of the unsaturated monomer, a remaining portion of the soap, and a redox initiator system; the contents of the vessel that are heated to between 54.4 ℃ (150 ° F) and 60 ℃ (140 ° F) when about fifty weight percent of the unsaturated monomer is introduced to the reaction vessel; the contents of the vessel being cooled to provide a copolymer encapsulated polytetrafluoroethylene latex dispersion, wherein the latex exhibits enhanced mechanical stability such that the latex does not undergo phase separation after stirring at 200rpm for at least 100 hours; the latex dispersion is coagulated to provide a copolymer resin.

Aspect 46. The system of aspect 45, wherein the initial charge comprises 45 to 55 parts by weight polytetrafluoroethylene, 1 to 20 parts by weight styrene, and 1 to 5 parts by weight soap and wherein the initial charge of soap is 1.25 parts by weight and the continuous charge of soap is 2.75 parts by weight.

Aspect 47. The system of any of aspects 45-46, wherein the unsaturated monomer is styrene or acrylonitrile.

Aspect 48. The system of any of aspects 45-47, wherein the unsaturated monomer is added to the initial charge after heating the vessel to 57.2 ℃ (135 ° F).

Aspect 49. The system of any of aspects 45-48, further comprising combining a chain transfer or crosslinking agent with the incorporation of the aqueous dispersion, the styrene monomer, and the soap.

Aspect 50. The system of any of aspects 45-49, wherein the initial charge or continuous feed comprises a molecular weight regulator.

Aspect 51. The system of any of aspects 45-50, wherein the latex comprises 25 wt.% to 65 wt.% solids.

Aspect 52. The system of any of aspects 1-12, wherein the output slurry is dried to produce a resin powder.

Examples

The following examples are provided to illustrate the compositions, methods, and properties of the present disclosure. These examples are illustrative only and are not intended to limit the disclosure to the materials, conditions, or process parameters described therein.

Table 1 shows typical components for a commercially available TSAN latex (comparative example 1).

Table 1: components of commercially available TSAN latex.

Table 2 shows the components of a new embodiment of the TSAN latex described in this disclosure (e.g., example 2).

Table 2: novel TSAN latex

In the presence of added monomer (styrene)) Previously, an initial charge comprising PTFE dispersion, water, t-dodecyl mercaptan (TDDM), and tallow fatty acid soap was heated to 54.4 ℃ (136 ° F). The mixture was pretreated for at least 15 minutes before initiating the reaction by continuous feed. As the temperature rises to 65.6 deg.C (150 deg.F), at mid-point, the remaining acrylonitrile and styrene monomers and redox initiator system [0.3 parts cumene hydroperoxide CHP, 0.003 parts ferrous sulfate, 0.03 parts tetrasodium pyrophosphate TSPP and 0.375 parts reduced fructose syrup in the portion associated with 100 parts total polymer (PTFE + styrene + acrylonitrile) ]]Addition was by continuous feed for 1.5 hours. Molecular weight regulators have also been introduced to regulate the molecular weight of the copolymers. The latex was prepared by mixing the latex in hot water at about 93.3 deg.C (200 deg.F) and sulfuric acid H as a coagulant₂SO₄To obtain TSAN resin. The resulting slurry was then centrifuged to separate the water and the resulting wet resin was dried to less than 0.5 wt% water content.

Table 3 shows the mechanical stability (MMS) of comparative example 1 and example 2. As shown in table 3, by reducing the amount of TFA soap added in the initial charge of the polymerization process, and then adding the remaining TFA soap to the continuous feed, the soap coverage increased from about 55% to about 69%. This modification of how much soap is added and when soap is added to the emulsion polymerization process results in a more than tenfold increase in MMS of the novel TSAN latex from 7 minutes to 75 minutes.

Table 3: comparison of mechanical stability of TSAN latex

The latex formulations of control 1 and example 2, all containing 39% latex solids, were also evaluated for long term stability to particle deposition using near infrared centrifugation techniques. LumiSizer Using multiple analytical centrifuges^TMControl 1 and example 2 were analyzed to simultaneously measure the intensity of transmitted light through the sample as a function of time to measure the extent of deposition. Each sample was measured twice (designated run 1 and run 2) to provide four transmission spectra, as shown in figure 1. Analytical centrifuge LUMiSizer^TMAllowing to apply a centrifugal force to the sample(particles relative to normal gravitational force

Acceleration of motion) accelerates the separation of the dispersion. The separation behavior of individual samples can then be compared and analyzed in detail by tracking changes in near infrared transmission through any portion of the sample or by tracking the movement of any phase boundaries.

LUMiSizer^TMThe analyzer results are shown in fig. 1. In particular, as by LUMiSizer^TMThe instability indices of comparative example 1 were 0.0008 and 0.0007, as quantified by the analyzer. However, TSAN example 2, two trials represented by two overlapping curves of the four curves shown in fig. 1, had a much lower instability index of 0.0003. These lower values indicate that the latex prepared from the disclosed formulation not only has enhanced mechanical stability, but also has an extended shelf life, compared to commercially available TSAN latexes. Table 4 provides the average values of the slopes observed in the tests of comparative example 1 and example 2, as well as the observed values. The instability index ranges from 0 to 1.0, with a value of zero indicating no instability. The lower the instability index, the more stable the dispersion.

Table 4: instability index of control and inventive samples.

Using a LUMiSizer^TMThe analyzer prepares transmission position spectra for two runs of each of control example 1 and example 2. The set of transmission curves was observed at different positions along the sampling vessel (cuvette) and the data obtained from the curves was reduced to a single curve by appropriate integration of the respective transmission percentages. The integration of these curves was used to infer the instability index shown in table 4. The stability of the latex was also used by examining the transmission spectrum. The horizontal segment of the curve shows that the latex sample under consideration does not change with respect to the transmission profile along the cuvette during the time interval under consideration. The ramp back traces back to sedimentation/creaming, i.e. latex instability. A sharp rise back or sudden change in the curve also indicates sedimentation or creaming. The curves of the two tests of comparative example 1 show the transmissionA sudden change in percentage. The curves for both experiments of example 2 were horizontal and showed a gradual change in the percent transmission. Thus, the transmission spectrum curve of example 2 corresponds to a higher stability in example 2 compared to the curve representing comparative example 1.

A TSAN latex was prepared according to the formulation in Table 1 (control example 3), and a TSAN latex was prepared according to the formulation in Table 2 (example 4). These latexes are labeled control 3 in fig. 3 and example 4 in fig. 4. Both latexes (39% TSAN) were subjected to laboratory scale coagulation simulation by stirring the dispersion at 200rpm for at least 100 hours with continuous agitation. The novel non-creaming nature of TSAN example 4 is demonstrated in fig. 4. In particular, 4 shows that TSAN example 4 latex is able to maintain its original viscosity throughout extended agitation (i.e., no creaming occurs despite continuous agitation for more than 100 hours) due to high mechanical stability (MMS) (55 minutes), while comparative example 3 latex was found to creame within 8.5 hours due to low MMS (only 2 minutes), as shown in figure 3.

Table 5 shows the unexpected effect of activator solution charging sequence on TSAN latex stability. If the activator solution is added by initial batch charging rather than continuous charging, its mechanical stability decreases significantly from 75 minutes to 7 minutes, while the soap coverage only decreases from 69% to 60%. The results indicate that the combination of initial/feed soap charge and continuous activator feed is critical to produce stable TSAN latex without creaming.

Table 5: effect of the order of activator Loading in the preparation of TSAN latex

Examples 7, 8, 9 and 10 in table 6 show that there is an important level of initial soap charge to obtain a stable TSAN latex. Examples 7 and 8 show that the MMS remained at about 10 minutes when the initial soap level was between about 4 parts to about 1.75 parts. But as shown in example 9, when the initial soap feed level was about 1.25 parts, the MMS increased to greater than about 30 minutes. Examples 9 and 10 show that stable latexes can be achieved by reducing the initial soap from 1 part to 0.5 part, even when the activator is a batch charge that tends to reduce MMS as shown in example 4. The formulation and charging sequence used in example 9 were selected as candidates to produce stable TSAN latex under prolonged agitation without the need for additional soap to prevent its creaming (irreversible premature coagulation due to poor stability).

Table 6: achieving the existing optimal initial soap level for stable TSAN latex

Example 2 (also example 9) was selected for scale-up to produce unsaponified TSAN latex with excellent MMS (MMS greater than about 60 minutes) without post-addition of TFA soap, as is typically done in existing latex production processes in processing equipment (comparative example 1). Table 7 summarizes the equipment test results. Production scale-up shows that the novel TSAN process improves soap coverage, latex stability and shelf life (lower instability index as observed in the novel TSAN latex without adding additional TFA soap after polymerization, whereas 3pbw or more TFA is required in the prior art process to prevent creaming thereof) while meeting all resin quality requirements with more consistent flowability. The plant test data also shows that the new process increases SAN conversion by about 1% (i.e., about 25% reduction in acrylonitrile emissions and about 65% reduction in styrene emissions).

Table 7: latex and resin Properties of novel TSAN and control TSAN

Claims

1. A polymerization process, comprising:

a. an initial charge comprising:

introducing an aqueous dispersion of polytetrafluoroethylene into a vessel;

introducing styrene or acrylonitrile monomer into the vessel;

introducing soap into the container;

heating the contents of the vessel to between 54.4 ℃ and 60 ℃; and

allowing the dispersion to pre-treat in a container for 15 minutes;

wherein the initial charge comprises introducing into the vessel 45 to 55 parts by weight of polytetrafluoroethylene, 5 to 20 parts by weight of styrene or acrylonitrile monomer, and 1 to 5 parts by weight of soap, and wherein the combined parts by weight value of all components does not exceed 100 parts by weight;

b. a continuous feed comprising:

introducing styrene and acrylonitrile monomers;

introducing a redox initiator system;

introducing a soap; and

when 50 weight percent of styrene monomer, acrylonitrile monomer, and a copolymer of styrene and acrylonitrile are introduced into the container, the contents of the container are heated to between 65.6 ℃ and 71.1 ℃,

wherein the continuous feed comprises 31 to 34 parts by weight of styrene monomer, 11 to 14 parts by weight of acrylonitrile monomer, and comprises 0.1 to 2 parts by weight of a redox initiator system, and 1 to 5 parts by weight of soap introduced over a period of 1 to 2.5 hours; and

wherein the polymerization process produces a styrene-acrylonitrile copolymer encapsulated polytetrafluoroethylene latex dispersion.

2. The process of claim 1, for providing a stabilized poly (polytetrafluoroethylene-styrene-acrylonitrile) (TSAN) resin, further comprising a coagulation process to isolate TSAN resin.

3. The method of claim 2, wherein the agglomerating comprises adding acid and water to a latex produced by a polymerization reaction.

4. The process of claim 2, wherein the isolated TSAN resin is dried upon isolation.

5. The method of any one of claims 1-4, wherein the initiator is a combination of cumene hydroperoxide, ferrous sulfate, tetrasodium pyrophosphate, and a reducing sugar.